Academy of Medical Sciences of I.R. Iran Archives of Iranian Medicine 1029-2977 29 4 2026 04 01 Trends and Age-Period-Cohort Effects on Gastric Cancer Mortality in the Iranian Population (1990–2023) 201 212 10.34172/aim.35592 EN Maryam Karimi Ghahfarokhi https://orcid.org/0000-0002-0822-9104 Majid Aminzare Fatemeh Masaebi https://orcid.org/0000-0002-8439-5024 Journal Article 10.34172/aim.35592 2025 12 16 2026 03 20 Introduction: Gastric cancer (GC) remains a major cause of cancer mortality in Iran, with clear disparities between males and females. This study provides a comprehensive evaluation of GC mortality patterns from 1990 to 2023 in Iran, focusing on how age, period, and birth cohort have shaped these trends through advanced statistical analyses. Methods: Age-specific and age-standardized GC mortality rates for the Iranian population, stratified by gender, were extracted from the Global Burden of Disease (GBD) Study 2023 for the years 1990 to 2023. Joinpoint regression and the Age-Period-Cohort (APC) model were applied to estimate the Average Annual Percentage Change (AAPC) and the Relative Risks (RRs), respectively. Results: The findings showed a significant decrease in GC mortality rates, with average annual percent changes of -2.26, -2.41, and -2.07 per 100,000 population for the total, female, and male populations, respectively. Additionally, the APC model revealed an upward trend in age and period effects, and a decreasing trend in cohort effect for both males and females. In the total population, the age effect increased, except for the 90-94-year group (RR=5.47, 95% CI: 5.37, 5.64, P<0.001). The period effect showed an increase from 1994 (RR=0.90; 95% CI: 0.89, 0.90) to 2023 (RR=1.20; 95% CI: 1.17, 1.21). The cohort effect showed a consistent decrease in mortality from earlier to later birth cohorts (RR=3.86 for the<1903 cohort vs. RR=0.19 for the 2004-2008 cohort). Conclusion: Gastric cancer mortality in Iran has declined over the past three decades; however, it remains higher among older individuals and men. The recent increase observed during 2014–2023 underscores the need for continued surveillance of temporal trends.